It is sometimes therapeutically desirable to occlude blood flow in one or more blood vessels of a human or animal subject. This circumstance may arise in a variety of clinical conditions, such as an acute bleeding episode. Such bleeding may occur from any organ after trauma, or may result from a variety of pathologic conditions such as ulcers, tumors, diverticulitis, portal hypertension, or postpartum hemorrhage.
In many such situations, an invasive surgical approach may be attempted. For example, after pelvic or abdominal trauma, a surgeon may perform open or laparoscopic surgery. The source or sources of bleeding may be identified, cauterized or ligated. However, surgical procedures carry substantial morbidity and mortality rates. There is often an emergent need to control bleeding in order to save the life of the subject, and the subject may expire during the time needed to prepare an operating suite, induce anesthesia, and perform the procedure. In addition, open surgery adds substantial additional stress for the subject.
Accordingly, health care practitioners have sought a more rapid and/or less invasive means of controlling bleeding. For example, a practitioner may access the interior of the subject's blood vessels by inserting a catheter via a percutaneous approach. A variety of sclerosing or embolic agents may be injected through the catheter, such as ethanol, microfibrillar collagen, Gelfoam, silastic beads, polyvinyl alcohol foam, or polymer resins. The use of some of these agents are described in U.S. Pat. Nos. 5,580,568; 5,667,767; and 6,059,766; Vedantham, et al., Am. J. Obstet. Gynecol. 176: 938–948, 1997; and Imembo, Diverticular Disease of the Colon, Sabiston: Textbook of Surgery, 15th ed., page 987, © 1997 W.B. Saunders Company. Other percutaneous alternatives include blood coagulation by endovascular delivery of local heat, either by laser or an electrical heating coil, for example, as described in U.S. Pat. Nos. 4,735,201 and 5,851,206.
In addition to control of bleeding, it also may be therapeutically desirable to induce thrombosis in pathologic vascular conditions such as aneurysms, arteriovenous malformations, and arteriovenous shunts, for example as described in U.S. Pat. Nos. 5,122,136; 5,354,295; and 5,894,022; O'Reilly et al., Radiology 171: 471–474, 1989; Kinugasa et al, J. Neurosurg. 77: 501–507, 1992; Taki et al., J. Neurosurg. 77: 37–42 1992; and Takebayashi et al., J. Urol. 159: 696–701, 1998. Blood vessels supplying a tumor represent another target for therapeutic thrombosis; see, for example, U.S. Pat. Nos. 6,093,399 and 6,015,541; and Castaneda-Zuniga, et al., Vascular Embolotherapy, in Interventional Radiology, Part 1, 1: 9–32, Williams & Wilkins, 1992. Such thrombosis may limit tumor growth or metastatic potential by reducing its blood supply.
In addition to blood vessels, it may also be therapeutically desirable to occlude the lumen of other hollow organs. For example, ligation or occlusion of the fallopian tubes of a female subject or the vas deferens of a male subject may provide effective contraception.
Radiofrequency energy has been used to occlude blood vessels, as described in U.S. Pat. No. 5,743,905; to treat vascular aneurysms, as described in U.S. Pat. No. 5,122,136, and to occlude other hollow organs such as fallopian tubes, as described in U.S. Pat. No. 5,556,396. However, energy delivery to the inner wall of the vessel may be imprecise, due to a failure of the electrode to conform optimally to the inner wall. Much of the electrode may not be in contact with the inner wall, but instead remains in the lumen. Instead of being delivered to the vascular wall, energy is dissipated into the blood stream. Thus, the vascular tissue may be incompletely cauterized, or alternatively, may be perforated by excessive energy delivery at an isolated contact point.
In addition to occluding lumens of hollow organs, under some clinical circumstances it may be therapeutically desirable to increase lumen diameter. For example, it may be desirable to reduce a stricture or stenosis in a bronchus, esophagus, a segment of intestine, or a blood vessel. In arteries, it may be desirable to reduce a stenosis that reduces blood supply to an organ, for example, a stenosis in a coronary artery that reduces blood supply to the working heart muscle. Moreover, it may be desirable to reduce a restenotic lesion, that is, a stricture or stenosis in a hollow organ that has recurred at least once after a procedure that reduced the severity of the stricture or stenosis. For example, an artery may develop a restenotic lesion after a successful angioplasty procedure at the site of an atherosclerotic stenosis. Such restenotic lesions may develop even when a stent is placed after angioplasty to prop open the vessel. When arterial restenosis occurs after stent placement, it is referred to as in-stent restenosis. Current therapeutic options for in-stent restenosis are limited, and surgery is often required.